Private equity firm Kenner & Company has tapped CIBC World Markets and UBS to provide a credit facility backing the $610 million acquisition of window-manufacturer Atrium Corp. An investor said the "B" piece is not expected to be too large, since the firm is likely to issue notes to refinance existing bonds. He said the bank debt could be less than $200 million. The new debt will also refinance existing bank debt. Atrium's current principal shareholders include affiliates of Ardshiel, a Greenwich, Conn.-based private equity firm, and GE Asset Management. Bankers at the lead firms did not return calls.